Forming polyethylene terephthalate

ABSTRACT

A PROCESS FOR FORMING A SHEET OF POLYETHYLENE TETRPHTHALATE INTO A MOLD CONFIGURATION, THE PROCESS COMPRISING (A) HEATING A SHEET OF POLYETHYLENE TEREPHTHALATE HAVING AN INTRINSIC VISCOSITY OF ABOUT FROM 0.50 TO 0.59 AND A DEGREE OF CRYSTALLIZATION OF ABOUT FROM 0 TO 25% TO A TEMPERATURE OF ABOUT FROM 75* TO 180*C.; (B) FORCING THE HEATED SHEET ONTO A MOLD SURFACE; AND (C) HEAT SETTING THE SHAPED SHEET AT A TEMPERATURE OF ABOUT FROM 125* TO 220*C. AND FOR A PERIOD OF TIME SUFFICIENT TO INCREASE THE DEGREE OF CRYSTALLIZATION OF THE FORMED ARTICLE TO ABOUT FROM 25 TO 60%. PARTICULARLY USEFUL ARTICLES THAT CAN BE FORMED BY THE PROCESS INCLUDE TRAYS HAVING A BOTTOM PANEL, SIDE WALLS CONNECTED TO THE BOTTOM PANEL AND A CONTINUOUS OUTWARDLY EXTENDING FLANGE CONNECTED TO THE UPPER EDGES OF THE SIDE WALLS; THESE TRAYS CAN BE USED FOR FOOD CONTAINERS, WHICH ARE HEATABLE IN EITHER CONVENTIONAL OR MICROWAVE OVENS AND ARE STRONG AND DIMENSIONALLY STABLE AT TEMPERATURES UP TO ABOUT 460*F. ADHESIVE CAN BE APPLIED TO THE UPPER SURFACES OF THE FLANGE TO PERMIT THE APPLICATION OF A COVER FILM TO THE TRAY.

DEFENSIVE PUBLICATION UNITED STATES PATENT OFFICE Published at therequest of the applicant or owner in accordance with the Notice of Dec.16, 1969, 869 0.G. 687. The

abstracts of Defensive Publication applications are identified bydistinctly numbered series and are arranged chronologically. The headingof each abstract indicates the number of pages of specification,including claims and sheets of drawings contained in the application asoriginally filed. The files of these applications are available to thepublic for inspection and reproduction may be purchased for 30 cents asheet.

Defensive Publication applications have not been examined as to themerits of alleged invention. The Patent Olfice makes no assertion as tothe novelty of the disclosed subject matter.

PUBLISHED OCTOBER 9, 1973 915 O.Gr. 883

T915,001 FORMING POLYETHYLENE TEREPHTHALATE David Harris Berkebile andKenneth Leith Knox, Circleville, Ohio, assignors to E. I. du Pont deNemours and Company, Wilmington, Del.

Continuation of abandoned application Ser. No. 81,312, Oct. 16, 1970.This application July 10, 1972, Ser. No. 269,948

Int. Cl. B29c 17/04, 25/00 US. Cl. 264-89 1 Sheet Drawing. 8 PagesSpecification A process for forming a sheet of polyethyleneterephthalate into a mold configuration, the process comprising (a)heating a sheet of polyethylene terephthalate having an intrinsicviscosity of about from 0.50 to 0.59 and a degree of crystallization ofabout from 0 to 25% to a temperature of about from 75 to 180 C.; (b)forcing the heated sheet onto a mold surface; and (c) heat setting theshaped sheet at a temperature of about from 125 to 220 C. and for aperiod of time sutficient to increase the degree of crystallization ofthe formed article to about from 25 to 60%. Particularly useful articlesthat can be formed by the process include trays having a bottom panel,side walls connected to the bottom panel and a continuous outwardlyextending flange connected to the upper edges of the side walls; thesetrays can be used for food containers, which are heatable in eitherconventional or microwave ovens and are strong and dimensionally stableat temperatures up to about 460 F. Adhesive can be applied to the uppersurfaces of the flange to permit the application of a cover film to thetray.

Oct. 9, 1973 D. H. BERKEBILE ET AL T915,001

FORMING POLYETHYLENE TEREPHTHALATE Original Filed Oct. 16, 1970INVENTORS DAVID H. BERKEBlLE KENNETH L. KNOX BY Q TTORNEY

